In at least some known epitaxial reactors used in processing semiconductor wafers, temperatures within the reactors are controlled by multiple proportional-integral-derivative (PID) controllers, each controlling a respective zone. For example, in some systems, an epitaxial reactor includes a first PID controller associated with a center zone, a second PID controller associated with a front zone, a third PID controller associated with a side zone, and a fourth PID associated with a rear zone.
Given that PID controllers are configured to control temperatures during steady state conditions, control errors may occur during transitions to new temperature set points. In particular, multi-PID arrangements controlling different zones that interact with each other, for example from heat originating from one zone and transferring into a neighboring zone, may be inadequate for controlling relatively fast state transitions. This is especially problematic when the relative balance between different zones needs to be precisely controlled throughout a transition. For example, during the processing of a semiconductor wafer in an epitaxial reactor, temperature gradients across the various zones may cause the wafer to experience thermal stress and develop defects, rendering the wafer unusable. Given these limitations, transitions to new temperature set points have to be prolonged to allow the PIDs to achieve the desired temperature set points without causing defects in the wafer. Accordingly, manufacturing throughput for semiconductor wafers could be increased if transitions to new temperature set points could be achieved in multiple-PID epitaxial reactors at increased speed.